Mortars (cf. for example Gerhard Stehno: "Baustoffe und Baustoff-prufung", Springer Verlag, Vienna 1981, page 82) are understood in the building industry to be mixtures of aggregates, binders and water and, if desired, additives.
Plasters are different from mortars. Plasters are normally understood to be mixtures of aggregates and binders and optionally additives. Accordingly, plasters are substantially "dry" systems. Plasters are converted into mortars by stirring with water. In practice, plasters are normally stirred with water, i.e. converted into mortars, just before use.
The above-mentioned ingredients or functional components of plasters and the mortars obtainable from them by adding water are as follows:
The so-called aggregates are generally mineral aggregates (sands) with a maximum particle size of 4 mm. The function of the sand is to form a mineral framework in the mortar. By suitably selecting the sand, it is possible favorably to influence both the volume stability and the strength of the mortar. In most cases, natural sand is used, although artificial sands may also be used.
Binders are selected according to the required processability and the required properties of the hardened mortar. By mixing the binder with water, the individual aggregate particles are supposed to be coated and cemented together. In general, two types of binder are used. First, there are the mineral binders. Mineral binders are divided into air-curing binders which cure exclusively in air after the addition of water, and hydraulic binders which can cure both in air and in water after the addition of water. Depending on the nature of the mineral binder, the corresponding mortars are known as gypsum mortars, gypsum lime mortars, anhydrite mortars, anhydrite lime mortars, plaster and masonry binding mortars, cement mortars and magnesia mortars. Besides the mineral binders mentioned, organic binders are also used. In their case, the corresponding mortars are also known as synthetic resin mortars.
By incorporating additives, certain mortar properties, for example permeability to water, particularly good adhesion, workability, color etc., can be influenced or improved.
Mortars can be classified in various ways. Typically, mortars are classified according to
a) the type of binder used (for example cement mortar, lime mortar, lime cement mortar, gypsum mortar, etc.), PA0 b) the application envisaged (for example masonry mortars, plaster mortars, Colgraut mortars, joint mortars, screed mortars, etc.) and PA0 c) the hardening process (for example non-hydraulic mortars or hydraulic mortars). PA0 by stirring the plasters containing the additives with water or PA0 by stirring the individual components (aggregates, binders and additives) with water,
The Following Observations Apply to Plaster Mortars:
Plasters are applied to walls and ceilings in one or more layers, according to requirements. Apart from the aesthetic appearance of the surface, plasters provide protection against the effects of weather (external plasters) and form a smooth surface for screeds and wallpapers (internal plasters); in steel-reinforced concrete ceilings and stairs and in steel stanchions, they protect the steel cores against fire and, where porous aggregates are used, afford protection against heat. Basically, internal and external plasters should be able to breath, i.e. should allow the exchange of moisture by vapor diffusion between the plastered components and the atmosphere. Plaster mortars are used for plasters containing mineral binders while coating materials (synthetic resin plasters) are used for plasters containing organic binders. Both can act in combination as a plaster system. Coating materials for the production of synthetic resin plasters often consist of organic binders in the form of dispersions or solutions and fillers in which most of the particles are larger than 0.25 mm in size. They are normally supplied in processable form.
A general problem with plaster mortars is that they dry out prematurely during processing. To prevent such premature drying out (which results in crack formation, etc.), for example under the effect of air and/or sunlight, it is normally proposed in the relevant literature to protect plasters by suitable measures. These include spraying with water, sunscreening for external plasters, closing the window openings in the case of internal plasters while allowing ventilation to evaporate the moisture (cf. Siefried Harig, Karl Gunther, Dietmar Klausen, "Technologie der Baustoffe--Handbuch fur Studium und Praxis", Verlag C. F. Muller, Karlsruhe 1990, page 114).
In recent years, so-called dispersion plasters which contain redispersible polymer powders as binders have acquired increasing significance. "Dispersion plasters" are so called because the corresponding binders are prepared from aqueous polymer dispersions which have been converted into a dry state, for example by spray drying. If a plaster containing such a binder is contacted with water, the polymers are redispersed, i.e. the mortar thus obtained now contains polymers as binder.
The increasing success of dispersion plasters is attributable inter alia to such advantages as better adhesion and elasticity and to their water-repellent character. However, in the plastering of relatively large surfaces, the open time of dispersion plasters is a critical factor, as already generally described above for plaster mortars. This is because, after drying accompanied by coalescence of the polymer dispersion, the resistance of the plaster to water reaches a first stage after which the plaster can no longer readily be dissolved with water. The consequences are visible starting points. The problem is greater, the more heavily textured the plaster (rubbing plasters, texture plasters).
U.S. Pat. No. 3,486,916 describes cement mixtures characterized by a delayed free water release rate. These mixtures are obtained by adding an aqueous emulsion of C.sub.14-20 fatty alcohols which form an evaporation-inhibiting film on the surface of the cast objects.
WO 95/04008 describes a dry cement with a reduced tendency to exude lime under the influence of weathering, the hydraulic cement containing 0.01 to 3% by weight of at least one C.sub.14-22 fatty alcohol.
SU 950 703 (Derwent Abstract 63154 K/26) describes mixtures of various fatty alcohols, hydrocarbons, soaps and fatty acid esters. These mixtures are used to protect the surface of freshly laid concrete against the over-rapid evaporation of water.
SU 652 154 (Derwent Abstract 88793 B/49) describes the pro-duction of concrete moldings. Freshly laid concrete is coated with a dilute aqueous solution of cetyl alcohol. This is said to reduce the water evaporation rate by a factor of 4 to 5. The fatty alcohol layer is subsequently removed.
DE-A-44 34 010 describes redispersible polymer powders containing amino-s-triazine/formaldehyde/sulfide condensates as effective protective colloids which are of importance in the spray drying of the corresponding polymer dispersions. According to page 3, lines 7 et seq., the redispersible polymer powders contain vinyl- or acrylate-based polymers as their principal component. The examples of suitable polymers mentioned include products of vinyl acetate, vinyl propionate, vinyl laurate, vinyl chloride, vinylidene chloride, straight-chain or branched vinyl esters containing 3 to 18 carbon atoms (versatates), acrylic and methacrylic monomers, more especially esters, and styrene and ethene which may be present in the form of homopolymers, copolymers, terpolymers and as graft polymers.
DE-A-44 21 270 describes aqueous fatty alcohol dispersions which contain C.sub.10-28 fatty alcohols, anionic surface-active compounds and nonionic surface-active compounds. The aqueous dispersions in question are suitable as antifoam agents and as additives for dispersion-bonded plasters. According to page 5, lines 14 to 20, these aqueous fatty alcohol dispersions increase the open time of dispersion plasters. In addition, the tendency of dispersion plasters to develop cracks is distinctly reduced where these dispersions are used. A reduction in water absorption and hence an increase in the hydrophobicizing effect of the plasters are further advantages. Finally, the plasters also lend themselves to coating and have high permeability to water vapor. However, DE-A-44 21 270 discloses only aqueous dispersions containing inter alia fatty alcohols to increase the open time of dispersion plasters. Accordingly, DE-A-22 21 270 discloses fatty alcohols in dispersion form as open time extenders for dispersion plasters which are packaged as water-containing pastes.